Do Plants Scream? Ultrasonic Sounds Recorded

For centuries, humans have viewed the botanical world as a silent backdrop to life on Earth. We assume that because plants do not have vocal cords, lungs, or mouths, they cannot make noise. However, groundbreaking research has shattered this assumption. A recent study published in the journal Cell reveals that plants do effectively “scream” when they are under stress. While you cannot hear it with your naked ear, the plant kingdom is actually quite noisy.

The Discovery at Tel Aviv University

In 2023, a team of researchers led by evolutionary biologist Lilach Hadany at Tel Aviv University in Israel published findings that changed how we understand plant biology. They discovered that plants emit distinct, high-pitched airborne sounds when they are stressed.

The researchers placed tobacco and tomato plants in a soundproof acoustic box and set up ultrasonic microphones capable of recording frequencies between 20 and 250 kilohertz (kHz). They then subjected the plants to two specific types of stress:

• Dehydration: They stopped watering the plants for several days.
• Physical Damage: They cut the stems of the plants.

The results were undeniable. The plants emitted sounds that were recorded and analyzed. To the human ear, the recordings (when pitched down to an audible range) sound remarkably like the popping of bubble wrap or the rapid clicking of a typewriter.

How Loud Are These Sounds?

These are not faint whispers. The volume of these “screams” is approximately 60 to 65 decibels. This is roughly the same volume as a normal human conversation. The only reason we do not walk through a garden hearing a cacophony of clicks is the frequency.

Humans generally hear frequencies up to about 16 kHz. The plants in the study emitted sounds in the ultrasonic range of 40 to 80 kHz. While this is far beyond human hearing, it is well within the hearing range of many animals, including mice, bats, and moths.

The Mechanism: How Do They Make Noise?

Since plants lack a larynx, they are not screaming in the way an animal does. The leading theory explains that this noise is a result of cavitation.

Plants have a vascular system called xylem, which acts like a series of tubes transporting water and nutrients from the roots to the leaves. When a plant is healthy and hydrated, these tubes are filled with a continuous column of water.

When a plant becomes dehydrated or the stem is cut, the water tension changes. Air bubbles form within the xylem tubes, expand, and then violently collapse. This physical process creates a shockwave within the plant tissue, which results in the popping sound detected by the microphones. It is similar to the noise made when you crack your knuckles, which is also caused by bubbles popping in the synovial fluid.

Different Stressors create Different Sounds

One of the most fascinating aspects of the Tel Aviv study was the use of machine learning. The researchers did not just record noise; they trained an algorithm to listen to it.

The AI was able to distinguish between different types of plants and different types of stress with 70% accuracy. The algorithm could identify if a specific recording was:

1. A tomato plant that was thirsty.
2. A tobacco plant that had been cut.
3. A control plant that was perfectly happy.

The pattern of the clicking changes based on the condition. For example, a tomato plant suffering from dehydration emits roughly 35 pops per hour. When the same plant is cut, the frequency of the popping changes significantly. This suggests that the sound contains specific information about the physiological state of the plant.

Who Is Listening?

If humans cannot hear these sounds, does the noise matter? Biologists argue that it matters immensely to the surrounding ecosystem. The world is full of creatures capable of hearing ultrasonic frequencies.

Animals

It is highly probable that animals use these sounds to make survival decisions.

• Moths: A moth looking for a place to lay its eggs might avoid a tomato plant that is emitting “thirsty” sounds. The larvae would struggle to survive on a dehydrated host, so the acoustic cues serve as a warning.
• Predators: Mice and bats might use these sounds to navigate or locate insects that prefer stressed plants.

Other Plants

The question of whether other plants “listen” is still under investigation. Previous research has shown that plants can respond to sound. For instance, some flowers increase the sugar concentration in their nectar when they detect the vibration of a bee’s wings. It is scientifically plausible that a healthy plant might detect the cavitation sounds of a nearby drought-stressed neighbor and close its stomata (pores) to conserve water in anticipation of dry conditions.

Is This Communication?

The snippet provided with this article rightly notes that this is likely not “communication” in the intentional sense.

Communication implies a sender intending to send a message to a receiver. The sounds emitted by these plants are likely a passive byproduct of physics (cavitation). It is an involuntary reaction to stress, similar to a human wheezing when they have a cold. The human isn’t trying to tell you they are sick by wheezing; the wheeze is simply what happens when airways are constricted.

However, just because the sound is involuntary does not mean it lacks information. In biology, these are called “cues” rather than “signals.” A signal is intentional (like a bird song); a cue is unintentional (like the sound of rustling leaves). The plants are broadcasting cues that other organisms can exploit for their own benefit.

Applications in Agriculture

This discovery has massive potential for the future of farming and food security. Currently, farmers often rely on visual inspections to determine if crops need water. By the time a plant looks droopy or brown, it has already suffered significant biological damage and growth has slowed.

By using acoustic sensors in greenhouses or fields, farmers could:

• Monitor hydration in real-time: Sensors could alert irrigation systems the moment the “clicking” frequency rises, watering crops exactly when they need it.
• Detect disease or damage: Since different stresses produce different acoustic patterns, AI monitoring could alert a farmer to a pest infestation (which causes physical damage) before it becomes visible to the eye.
• Save Water: Precision irrigation based on plant acoustic feedback could drastically reduce water waste in agriculture, which is currently a major global resource issue.

Frequently Asked Questions

Can I hear my house plants screaming? No. Unless you have specialized ultrasonic recording equipment capable of detecting frequencies above 20 kHz, your house plants will remain silent to you.

Do all plants make these sounds? The study focused on tomatoes and tobacco because they are easy to grow and analyze, but the team also recorded sounds from wheat, corn, Cabernet Sauvignon grapevines, henbit, and pincushion cacti. It is highly likely that this is a universal trait among vascular plants.

Does this mean plants have feelings? No. The emission of sound is a physical process caused by air bubbles in the vascular system (cavitation). It is a mechanical response to physical stress, not an emotional response to pain.

How often do they make the sound? Unstressed plants are very quiet, emitting less than one pop per hour. Stressed plants become much more active, with some species emitting 30 to 50 pops per hour depending on the severity of the dehydration or damage.